I'm an actor, and when I'm between roles, my bread-and-butter is something called ADR – additional dialogue recording – where I go to a studio and record background conversations for scenes from films in post-production. It's often a restaurant scene. You stand at the microphone with another actor, watch a video of the sequence, pick two characters at a table in the background and improvise.

Last summer, I was invited to do ADR for Shame. At the time, we knew nothing about the film. My agent said: "It involves sexual sounds. Do you mind?" I said: "No, it's just a job. It's fine."

The sound engineer kept the sexual stuff till the end. There's a scene where Michael Fassbender's character goes to a gay club. At the back of some shots, couples were at it. So I stood at the microphone with another guy and we improvised. For example: "Yeah. YEAH. Go deeper, GO DEEPER." The sound engineer would say: "OK, a bit more intense, please." You came up with anything you could think of. "Who's your daddy?" Stuff like that.

One of the more entertaining moments came when we had to evoke the sound of a penis entering an open mouth. The engineer was almost embarrassed but we found it amusing. None of us had done anything like that before, but it was a hoot. There was a kind of one-upmanship.

The art of ADR is to make the noises blend in, so when I saw the finished film, I couldn't make out my own voice. I thought the film was terrific. I'm not sure how much I cared about the main character, but it was beautifully acted. And the ADR was great.